Abstract
To evaluate the amount of pyroglutamic acid formation during the synthesis of glutamic acid containing peptides, resin beads were substituted by known amounts of Fmoc-Glu(O(t)Bu)-Phe-Ala-NH2 and the corresponding side- product Pyr-Phe-Ala-NH2 and directly analyzed by time of flight-secondary ion mass spectrometry. Detection and quantification of pyroglutamic acid was achieved without release of the peptide chains in solution.